Electric motors of work machines are at risk of overheating the motor winding, whereby overloading, poor power grid quality (undervoltage/overvoltage), hindered cooling, a blocked rotor, or the like are the most common reasons for failure. Motors with a high utilization capacity, such as refrigeration compressor motors, are subject to forced cooling, and must be provided with special protection from such risks.
A protective device for temperature monitoring using a measuring circuit is known from DE 10 2014 107 170 A1, having a quantitative temperature sensor and at least one qualitative temperature sensor that are situated at a suitable location, for example in the winding of the motor. The protective device also has a triggering device with an evaluation device in order to evaluate the measuring signal that results from the total resistance of the measuring circuit, and to generate an output signal for the triggering device as a function of the measuring signal.